In one known type of transfer feeder incorporated in a transfer press and intended for conveying workpieces (mainly steel sheets) from one process station to another in the transfer press, workpiece suction means such as vacuum cups are employed and a workpiece is conveyed being absorbed by them.
Transfer feeders employing such workpiece suction means have been disclosed, for example, in Japanese Patent Publication No. 46291/1990; Japanese Patent Applications Laid Open Nos. 284731/1990, 299729/1990, 5030/1991; and Japanese Utility Model Publication No. 37463/1990.
In these known transfer feeders, in order to successively convey workpieces from one process station to another, it is necessary to synchronize the conveyance of each workpiece. Therefore, these known transfer feeders include a long beam on which a plurality of transfer bars having workpiece holding means such as suction cups are spaced at given intervals, and the operation for vertically moving all the transfer bars (cross bars) at a time and the operation for conveying workpieces by a specific distance are accomplished by such a construction that the long beam is connected, at one end thereof, to a rocking lever which is driven by a cam. In most of these transfer feeders, a gear mesh driving mechanism is used in combination with the above arrangement for the vertical or transverse movement of the beam.
Such conventional transfer feeders incorporated in a
(1) Since a plurality of transfer bars are moved up and down with the help of a long heavy beam, a considerable torque is generated on a cam shaft of a lift cam in the driving mechanism when the transfer bars are lifted. This requires a large driving force.
(2) When moving a plurality of transfer bars vertically, side play vibration occurs on a lift rod for supporting the long heavy beam, decreasing accuracy in positioning workpieces to be conveyed or causing noise.
(3) Further, dummy cams are required for eliminating the aforementioned undesirable torque generated on the lift cam shaft. This disadvantageously increases the manufacturing cost of a driving mechanism.
(4) High fabrication accuracy is required because of the provision of a gear meshing mechanism at a vertical driving region and at a transverse driving region for conveyance. This increases the manufacturing cost of a transfer feeder.